Staphylococcus Flashcards
Staphylococci
Gram Positive cocci
Occur in singles, pairs, tetrads, short chains, but most commonly as irregular clusters
Suppurative (Pus-forming) infections
Members of the group Pyogenic Cocci
More than 50 species and subspecies
Most common is S. aureus
Catalase Test
Production of oxygen form hydrogen peroxide
Is used to distinguish Staphylococcus (Positive) from Streptococcus (negative)
Pathogenic Species
S. aureus
S. pseudintermedias
S. hyicus
Double Zone Hemolysis
On blood agar S. aureus and S. pseudintermedius produce two zones of hemolysis.
A narrow zone of complete hemolysis (a-hemolysis)
Wider zone of partial or incomplete hemolysis (B-hemolysis)
Staphylococcus aureus
“golden yellow” colored collonies
Grows well in medium containing 7.5-10% NaCl
Mannitol Salt agar is routinely used to selectively isolate S. aureus and distinguish from S. epidermidis.
Opportunistic and nosocomial pathogen.
Causes enteritis (Food poisoning; intoxication)
MRSA
Methicillin resistant S. aureus
Major clinical and epidemiological problem in human hospitals.
Also present in animals and are of zoonotic significance
Habitat
Occur in commensals of the skin of humans and animals.
Rugged cell wall allows them to withstand environmental insults such as drying, heat, high concentrations of salts.
Virulence Factors
Most of them have been studied.
Cell-Associated Components,
Exoenzymes and Exotoxins
Virulence Factors:
Cell-Associated Components:
Protein A
Surface protein that binds to Fc region of IgG molecules, disrupts opsonization and phagocytosis
Virulence Factors:
Cell-Associated Components:
Capsular Polysaccharides
11 serologically distinct capsule types in S, aureus of Humans and Cattle
Interfere with host defense mechanisms by inhibiting attachement of antibodies, induce the release of cytokines, and mediate binding to epithelial and endothelial cells
Virulence Factors:
Cell-Associated Components:
Peptidoglycan and Lipoteichoic Acid
Cell wall components function as virulence factors probably by stimulating cytokine release
Virulence Factor:
Cell-Associated Components:
Adhesins
Proteins of the cell surface promote attachement to host proteins, such as fibronectin. (Fibronectin-Binding Protein responsible for attachement to blood clots)
Besides binding to host matrix proteins, the adhesins are responsible for the formation of Biofilm
Virulence Factor:
Exoenzymes:
Coagulase
Enzyme binds to prothrombin to form a complex called Staphylothrombin.
Protease activity is activated in the complex, leads to conversion of fibrinogen to fibrin
Localized clotting protects bacterial cells from phygocytic and immune defenses
Virulence Factor:
Exoenzymes:
Lipase
Enzyme hydrolyzes lipid molecules that the host produces in response to infections.
Act as surfactants and disrupt bacterial cell membranes, especially when an abscess is formed
Virulence Factor:
Exoenzyme:
Hyaluronidase
Enzyme digest hyaluronic acid present in connective tissue and promotes spread of the infection
Virulence Factor:
Exoenzymes:
Proteases
Best described staphylococcal protease is a serine protease (V8 protease)
Cleaving and inactivating antibodies, antimicrobial peptides, and to obtain nutrients.
Contribute to tissue protein destruction and enhance invasiveness
Virulence Factor:
Exotoxins:
Toxic Shock Syndrome Toxin (TSST-1)
Superantigen activity
Stimulate T cells nonspecifically without normal antigenic recognition resulting in a strong stimulation of T cells, which respond with proliferation and massive cytoline release
Virulence Factors:
Exotoxins:
Enterotoxins
toxins are responsible for diarrhea and vomiting when ingested in fodd poisoning caused by S. aureus.
May also have Superantigen activity
Major cause for food-borne disease
Toxin is resistant proteases, heat stable, and not inactivated by cooking. The toxin in ingested with the food, and in the stomach the toxin stimulates vagus nerve endings to induce vomiting and abdominal pain.
Virulence Factor:
Exotoxin:
Exofoliative or Epidermolytic Toxins
Cause a spectrum of skin diseases, ranging from bullous impetigo to the scaled skin syndrome in humans.
S. hyicus causes exudative or exfoliative dermatitis (greasy pig disease)
Virulence Factors:
Extotoxins:
Hemolysis
- Alpha Toxin
- most potent membrane-damaging pore-forming toxin.
- Narrow zone of complete hemolysis surrounding the colony on sheep or cattle blood agar
- Beta Hemolysin
- Sphingomyelinase, damages membranes rich in sphingomyelin lipid.
- Responsible for incomplete hemolysis of sheep or cattle erythrocytes
- Gamma Toxin
- Leukotoxin, toxic to leukocytes.
- Important virulence factor in necrotizing lesions.
- genes located on a prophage
- Delta Toxin
- small peptide.
- Role in disease not known
- Pro-inflammatory toxin
Antibiotic Resistance
- Beta-lactamase
- enzyme that hydrolyzes b-lactam ring of penicillins ans cephalosporins
- Penicillin-binding Protein 2a (PBP2a)
- confers resistance to penicillins and cephalosporins-class of antibiotics.
Pathogenesis and Pathogenic Mechanism
Pyogenic bacteria that cause suppurative lesions.
Minor injury to the skin or immune suppression is a predisposing factor for the development of infections.
Pathogenic effects can range from minor local infections to life-threatening septicemic conditions
Mastitis in Dairy Cows
accounts for 25-30% of mastitic infections,
